Quantum memories (QM) for
light, which allow a coherent and reversible transfer of quantum
information between light and long lived matter quantum bits, are
crucial devices in quantum information science [1]. In particular
they enable to interface stationary quantum bits (encoded in
atom-like systems) and flying qubits (encoded in photons). QMs are
for example needed for the implementation of ultra-long distance
quantum communication using quantum repeater architectures [2]. An
important capability for quantum memories is the ability to store
multiple qubits at the same time and retrieve them selectively. Laser
cooled atomic gases are currently one of the best systems for QM
applications, but so far temporal multiplexing with quantum
information has not been achieved in these systems. In this
contribution, we show a significant step towards achieving this goal.
Our experiment is based on a type of QM that has proven to be one of
the most advanced quantum repeater building blocks [3], and consists
on a laser cooled Rubidium atomic ensemble where we create correlated
photon pairs. One of the photons is directly emitted while the other
one can be stored in the form of a single collective atomic spin
excitation (spin wave) before being mapped into a single photon.
Applying a controlled and reversible dephasing to the spin wave
allows the creation of photon-spin pairs in different temporal modes
and to map into a single photon only the desired spin excitation [4].
So far we have been able to observe the controlled dephasing and
rephasing of single spin waves. This has allowed us to perform a
selective mapping into photons between collective single spin
excitations created at two different times in the same atomic
ensemble. Our next goal is to use this system to demonstrate the
operation of a building block for a temporally multiplexed quantum
repeater protocol, which promises a significant rate enhancement.